The invention relates to a method for connecting shell parts that were produced, for example, by a deep drawing method of a sheet metal.
Shell parts made from sheet metal have many uses, for example, in the construction of vehicle bodies. The connection of shell parts can be performed, e.g., by stamped rivets, by spot-weld connections, or by beading or folding the sheet metal edges.
From DE 100 28 706 A1a device for turning over a bead edge of a work piece through roller folding with a drivable tool unit is known. The tool unit is mounted rotatably, so that several working positions can be assumed. The device comprises several folding rollers that fold the work piece in several steps one after the other. The pressure exerted on the folding edge in the last folding stage defines the strength of the folded seam connection. It has been shown, however, that the strength of the folded seam connection that can be achieved with this and similar methods is not sufficient for many applications. Alternating load conditions lead to micro-movements between the connected work pieces. These micro-movements lead to material wear in the joint gap that initially damages the usually provided corrosion protection. This can lead to corrosive attack on the base material, so that the joint gap continues to become bigger and the folded seam connection finally detaches.
From DE 100 33 768 A1, a method for folding thin-walled semifinished products or components made from metallic material is known, wherein the material is brittle and/or hard to shape at room temperature. The material involves, in particular, aluminum, magnesium, and titanium alloys. In the solution, the region to be folded is heated. The strength that can be achieved in a folded seam connection with brittle materials, however, is limited.
From DE 103 31 205 A1, a device and a method for turning over a bead edge of a work piece through roller folding is known. This solution is distinguished in that a heating device is provided that heats at least one region of the bead edge currently to be folded directly or indirectly during a folding process. An adhesive arranged in the folded seam of the work piece is thickened by the applied heat. In this way, the processes of folding and thickening usually performed one after the other are combined into one work cycle. Furthermore, the heating of the work piece simplifies the shaping, because the molecular lattice structure can be more easily adapted to deformation under the application of heat. The strength of the folded seam connection is defined, in particular, by the properties of the adhesive. In so far as no adhesives are used, the strength that can be achieved with this solution is in turn limited by the pressure on the bead edge that can be achieved by the rollers.